Silver halide photographic materials are generally composed of an electrically insulating support and photographic layers coated thereon. Such a structure promotes the formation and accumulation of static charges when subjecting the photographic materials to friction or separation, caused by contact with the surface of the same or different materials during steps for manufacturing of the photographic materials or when using them for photographic purposes. These accumulated static charges cause several drawbacks. The most serious drawback is discharge of accumulated charges prior to development processing, by which the light-sensitive silver halide emulsion layer is exposed to light to form dot spots or branched or feathery linear specks when development of the photographic film is carried out. This is the phenomenon of the so-called "static marks". Such static marks cause a reduction of the commercial value of photographic films, which sometimes become completely useless. For example, the formation of static marks in medical or industrial X-ray films may result in a very dangerous judgment or erroneous diagnosis. Static marks are a particular problem because it becomes evident for the first time by carrying out development. Further, these static charges are also the origin of secondary problems such as adhesion of dusts to the surface of films, uneven coating, and the like.
As mentioned above, such static charge are frequently accumulated when manufacturing and/or using silver halide photographic materials. For example, during production, they are generated by friction of the photographic film contacting a roller or by separation of the emulsion surface from the support surface during a rolling or unrolling step. Further, they are generated on X-ray films in an automatic apparatus by contact with or separating from mechanical pads or fluorescent screens, or they are generated by contact with or separation from rollers and bars made of rubber, metal, or plastics in a bonding machine or an automatic developing machine or an automatic developing apparatus or in a camera in the case of using color negative films or color reversal films. In addition they can be generated by contacting with packing materials, and the like.
Silver halide photographic materials having high sensitivity and handling speed are subject to an increase of static mark appearance. In particular, static marks are easily generated because of high sensitization of the photographic material and severe handling conditions such as high speed coating, high speed exposure, and high speed automatic processing.
In order to prevent problems caused by static charges, it is suitable to add an antistatic agent to the silver halide photographic materials. However, antistatic agent conventionally used in other fields cannot be used freely for silver halide photographic materials, because they are subjected to various specific restrictions due to the nature of the photographic materials. More specifically, the antistatic agents which can be used in silver halide photographic materials must have excellent antistatic abilities while not having adverse influences upon photographic properties of the photographic materials, such as sensitivity, fog, granularity, sharpness. Further, such antistatic agents must not have adverse influences upon the film strength and upon antiadhesion properties. Furthermore, the antistatic agents must not accelerate exhaustion of processing solutions and not deteriorate adhesive strength between layers composing the silver halide photographic material.
In the art of silver halide photographic materials a wide number of solutions to the above described problems have been suggested in patent and literature references, mainly based on charge control agents and electrically conductive compounds coated on the silver halide emulsion layer together with a binder as an antistatic layer.
The most useful charge control agents known in the art are ionic and non-ionic surfactant as well as ionic salts. Fluorinated surfactants are often mentioned as good antistatic agents in silver halide photographic materials.
Electrically conductive compounds are mainly focused on conductive polymers such as ionic polymers and electronically conductive polymers.
The use of ionic and non-ionic surfactant as well as fluorinated surfactants is widely disclosed in many patents, such as, for example, U.S. Pat. Nos. 2,600,831, 2,719,087, 2,982,651, 3,026,202, 3,428,456, 3,457,076, 3,454,625, 3,552,972, 3,655,387, 3,850,640, 3,850,642, 4,192,683, 4,267,265, 4,304,852, 4,330,618, 4,367,283, 4,474,873, 4,510,233, 4,518,354, 4,596,766, 4,649,102, 4,703,000, 4,847,186, 4,891,307, 4,916,054, EP 245,090, 300,259, 319,951,370,404, and the like.
The use of conductive polymers is widely disclosed in many other patents, such as, for example, U.S. Pat. Nos. 2,882,157, 2,972,535, 3,062,785, 3,262,807, 3,514,291, 3,615,531, 3,753,716, 3,769,020, 3,791,831, 3,861,924, 3,938,999, 4,147,550, 4,225,665, 4,363,872, 4,388,402, 4,460,679, 4,582,783, 4,585,730, 4,590,151, 4,701,403, 4,891,308, 4,960,687, EP 35,614, 36,702, 87,688, 391,176, 391,402, 424,010, GB 815,662, 1,222,595, 1,539,866, 2,001,078, 2,109,705.
In particular U.S. Pat. No. 4,649,102 discloses the combination of a non-ionic surfactant and an anionic surfactant having a polyoxyethylene group therein, U.S. Pat. No. 4,847,186 discloses the use of a fluorinated ionic or non-ionic compound, EP 245,090 discloses the combination of an organic fluoro compound and a polyoxyethylene non-ionic surfactant, U.S. Pat. No. 3,850,640 discloses the combination of a first layer comprising an anionic surfactant and a second layer comprising cationic and non-ionic surfactants, U.S. Pat. No. 4,596,766 discloses the combination of a polyoxyethylene non-ionic surfactant and a fluorine-containing compound, U.S. Pat. No. 4,367,283 discloses the combination of a polyoxyethylene non-ionic surfactant, a sulfonated surfactant, and a fluorine-containing phosphate surfactant, GB 2,246,870 discloses the combination of a polyoxyalkylene compound and a polystyrenesulfonate compound.
The use of copolymers of styrenesulfonic acid and maleic acid in antistatic layers different from silver halide emulsion layers is specifically disclosed in U.S. Pat. Nos. 4,460,679, 4,585,730, 4,891,308, 4,960,687 wherein a cross-linking agent is used in combination therewith, and in EP 391,402 and EP 391 176.
However, many of these substances and combinations thereof exhibit great specificity, depending upon the kind of film support or the photographic composition. Although some substances produce good results on certain specific film supports, photographic emulsions or other photographic elements, they are not only useless for preventing generation of static marks when using different film supports and photographic elements, but also have an adverse influence upon photographic properties.
On the other hand, there are many cases wherein, although they have excellent antistatic effects, they cannot be used due to their adverse influence upon photographic properties such as sensitivity, fog, granularity, sharpness, and the like.
For example, it has been well known that polyethylene oxide compounds have antistatic effects, but they often have an adverse influence upon photographic properties, such as an increase in fog, desensitization, and deterioration of granularity, in particular in silver halide photographic materials in which both sides of the support are coated with silver halide emulsions, such as medical X-ray photographic materials.
The use of fluorinated surfactants for controlling the electricity generation caused by friction or contacting with different materials, such as, for example, rollers, increases the charging in negative polarity. Accordingly, although it is possible to adapt the electric characteristics of the silver halide photographic material for each roller, such as, for example, rubber rollers, Delrin.TM. rollers, and nylon rollers by suitably combining the fluorinated surfactants with surfactants, charging in positive polarity problems still occur, because a general solution for all kind of rollers cannot be obtained.
Moreover, the market requirement of silver halide photographic material having a reduced processing time has increased the problems of static charges due to the higher speed to which silver halide photographic materials go trough the automatic processors.
Furthermore, the increasing demand of the radiographic market of medical X-ray silver halide photographic material, due to the increase in the worldwide consumption and diffusion of apparatus for X-ray diagnosis, requires an increase in productivity of medical X-ray photographic material that can be obtained with an increase of coating speed. Higher coating speed increases the appearance of static charges, if conventional antistatic agents are used.